Put the tamarind paste in a small bowl,
pour over the boiling water and stir well to break up any lumps. Leave
for 30 minutes. Strain, pushing as much of the juice through as
possible. Measure 6 tbsp of the juice, the amount needed, and store the
remainder in the fridge. Heat the oil in a wok. Add the chopped onion
and fry until golden brown.

Add the
sugar, stock, fish sauce, dried chilies and the tamarind juice, stirring
well until the sugar dissolves. Bring to the boil. Add the shrimps,
garlic and shallots. Stir-fry until the shrimps are cooked, about 3-4
minutes. Garnish with the spring onions.

Serves 4-6

The sour, tangy flavor that is
characteristic of many Thai dishes comes from tamarind. Fresh tamarind
pods from the tamarind tree can sometimes be bought, but preparing them
for cooking is a laborious process. The Thais, however, usually prefer
to use compressed blocks of tamarind paste, which is simply soaked in
warm water and then strained.